Hi, I have an 07 Star. The pumps are located behind the cover right at the rear behind the engine. To manually tell if the tanks are full, you only need to see the water pissing out the side of the boat half way along. The rear tanks take about 2 mins to fill, and the centre KGB about 5 mins to fill. No need to watch the ballast gauges ....

Your ballast tanks empty and fill from beneath the boat. The side ports are vents. The water from them are an overfill situation.
You might see bubbles if the tanks are empty and the pump remains on empty.

Yes, on the 07 the tanks empty under the boat, from the same fill pickup. You won't see anything. The pumps will make a different noise when the tank is empty... Try running the empty when the boat is on the trailer too to check.

As mentioned by robpout, you should hear a definate change in sound in the ballast pump as it goes from pumping water out the bottom of the boat to sucking air from the empty tank. At this point the pump is spinning faster due to the reduced strain - higher rpms of the pump = higher pitch noise. You can test this by filling the tanks for a little (you should hear going from a higher pitch sound to a lower pitch sound once the ballast pump primes), then reverse the switch and when the tank empties (pump looses its prime and rpms increase) and you will hear the sound change again. Once you get to know the sounds the ballast pumps make, you will know if they are empty or not just by the sound.

Also, if you have the pump AI timers/controls (and you should unless someone modified and removed them) the AI timer/control should observe the tank is empty (sensing the amperage change) after a short time (oh 5-10 seconds, maybe a little more) and your pump will automatically stop and the switch should display 1 blink. It is always nice to confirm the tank actually empty by observing the change in sound.

Since you are new, the thread link posted above is the single post view. To see the entire thread it was posted in, click on the "thead" link in the upper right hand corner to read more about the ballast timers.

Also, if you search on "ballast timers" you will find lots of information on this subject.